Listeria monocytogenes in Smoked Fish Production

Introduction: Reported cases of listeriosis have increased in the UK over the last decade. Although the overall incidence of listeriosis is small (4 cases /mil in 2007), the disease affects especially vulnerable groups (e.g., elderly people) with high mortality (up to 40%). The majority of cases appear to be sporadic and therefore it is difficult to identify the source of disease. Smoked fish (salmon, mackerel, herring and white fish) are a potential source of listeriosis, because the multiplication of pathogens (Listeria monocytogenes) can occur even under vacuum packaging conditions at refrigeration temperatures. 

Purpose: This study investigates management practices for reducing the risk of L. monocytogenes in the Scottish smoked salmon industry by gathering questionnaire information from factory and farm visits as well as collation and analysis of Listeriadata along the processing chain.

Methods: Sixteen visits to smoked salmon premises were conducted between June and November 2011, interviews were carried out based on a questionnaire.

Results: The results indicate that most processors carry out appropriate food safety practices, but some improvements are needed in order to minimize the risk of Listeria contamination. Improvements in refrigerated storage were required for some producers because of the risk of condensation dripping onto product from the ceiling. Small food business operators require additional information on how cleaning and sanitation throughout the process can reduce contamination of the final product. Furthermore, guidance describing the best way of determining shelf life was requested by small processors. Fifty-six percent of the smoked salmon producers (mostly large and medium size) tested the product for Listeria monocytogenes and the prevalence ranged between (0 to 12%) between producers.  Most processors rarely exceeded (i.e., once every several years) the statutory limit set by the European Union (>100 CFU/g or presence in 25 g). The small producers did not undertake product testing for Listeriabecause of high test costs and lack of technical expertise.

Significance: This study obtained a snapshot of the levels of Listeria in smoked salmon as well as industry practices. It was concluded that sharing expertise between producers, especially to smaller processors would be beneficial in terms of consumer protection. The study highlighted the need to provide training through workshops and information by an interactive web-based tool.